The study of sexual physiology—what happens, and why, and how to make it happen better—has been a paying career or a diverting sideline for scientists as far-ranging as Leonardo da Vinci and James Watson. The research has taken place behind the closed doors of laboratories, brothels, MRI centers, pig farms, sex-toy R&D labs, and Alfred Kinsey’s...

“What happens when we die? Does the light just go out and that’s that—the million-year nap? Or will some part of my personality, my me-ness persist? What will that feel like? What will I do all day? Is there a place to plug in my laptop?”

In an attempt to find out, Mary Roach brings her tireless curiosity to bear on an array of contemporary and...